Why is there no great temptress figure in any of Tolkien’s major works?

In addition to his religious themes, Tolkien folks are largely monogamous and traditional in matters of union and love; they only had one partner in life and many were not engrossed in loving affairs.

Tales of lust were rare, maybe very rare, but far from non-existent. So it is unlikely that tempting figures of both sexes did not exist; they are just not described greatly by the author. The most obvious cases I can think of would be some Maiarin servants of Melkor who assumed deceptive forms, male and female, to spy and induce treachery among the Elves and Men of Beleriand. Many must have been their means of argument.

Sources: The History of Middle-earth Vol 10. Morgoth’s Ring

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Other cases would be among the Elves, almost ethereal and pure as they were Tolkien still says that lust existed among them:

By the same reason that sex is rarely discussed, and homossexuality is inexistent.

Tolkien says, however, that guile or trickery in this matter was scarcely possible (even if it could be thought that any Elf would purpose to use it); for the Eldar can read at once in the eyes and voice of another whether they be wed or unwed.

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But if even among the Elves this was possible, among Men it must have been much more frequent, although again none of the known tales emphasize this much. In Númenor, it is said that many women gained fame as dancers. Númenoreans were largely free of these things for most of their history, but they fell into many evils in later days; drunkenness, gluttony, pride, violence, lust of many forms, etc.

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The Eldar wedded once only in life, and for love or at the least by free will upon either part. Even when in after days, as the histories reveal, many of the Eldar in Middle-earth became corrupted, and their hearts darkened by the shadow that lies upon Arda, seldom is any tale told of deeds of lust among them. Marriage, save for rare ill chances or strange fates, was the natural course of life for all the Eldar.

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This mean not that there were not tales of lust, treason, trickery, and guile. Even the most puritan fan will concede that there is a difference between how the author portrays his world and how it really was in-universe.